Systems that require positioning, navigation, and timing in order to function with full effectiveness rely on time and frequency subsystems (TFS). Performance of these systems requiring accurate timing may suffer due to vulnerabilities in the time and frequency subsystem from which timing is derived. Time and frequency subsystems typically obtain timing from a Global Navigation Satellite System (GNSS) receiver, such as a Global Positioning System (GPS) receiver, but can also obtain timing from other radio frequency (RF) sources. Such receivers are vulnerable to anomalies in the RF signals, which are difficult for the receiver to detect.
These anomalies can be the result of natural or human-made interference (such as a spoofing attack). Natural interference includes radio frequency (RF) noise, often generated from nearby transmitters or electrical equipment. Space weather events such as solar radio bursts can also produce natural interference. Human-made interference includes jamming and spoofing. A jamming attack is the intentional transmitting of RF signals by an adversary to disrupt or over-power reception of legitimate GPS RF signals by the targeted system. A spoofing attack is a technique used by an adversary to masquerade or falsify GPS RF signals, unknown to users of the targeted system. Additionally, unintentional spoofing can be caused by a faulty or misconfigured nearby device re-radiating GPS RF signals, such as a GNSS repeater. In subsequent paragraphs, the term “anomaly” refers to all types of RF signal interference and spoofing.
A Global Navigation Satellite System (GNSS), such as the Global Positioning System (GPS), entails a number of satellites that broadcast RF signals from which positioning, navigation, and timing (PNT) can be derived by receivers. For example, GPS satellites broadcast data encoded in RF signals. There are several codes used by GPS, and they are being continually improved. Two of these codes are the P-code, which is encrypted and generally used by the military; and the C/A code, which is not encrypted and generally used by civil infrastructure. The GPS receiver uses the data encoded in the GPS signals to determine PNT. A GNSS spoofing attack involves an attempt by an adversary to deceive a GNSS receiver, such as a GPS receiver, by broadcasting a signal which is different than the legitimate signals received from the GNSS satellites. Using GPS as an example, the broadcast signals are designed to appear as normal or standard GPS signals. However, the spoofed signals are modified in such a manner as to cause the GPS receiver to produce inaccurate time or timing intervals and/or produce a position at a location determined by the attacker, as opposed to the actual universal coordinated time (UTC) time or the receiver's actual location. Thus, the goal of spoofing is to provide a GPS receiver with misleading signals and therefore deceive the receiver to use fake signals for positioning and timing calculations, which will not be accurate.
The high reliance on GPS within civil infrastructure is an inherent security vulnerability. Individuals, groups, or nations interested in causing harm can target the GPS-based timing subsystem to attack a GPS reliant system, thereby potentially disrupting or disabling swaths of infrastructure including national critical infrastructure such as the financial and power industries, as well as communications and information technology networks, especially cellular communication systems. In particular, the concern is over GPS spoofing, an insidious form of intentional attack whereby a spoofer transmits counterfeit GPS signals to an unsuspecting (and unprotected) receiver. Spoofing is more malignant than jamming, because current civil receivers trust all GPS signals to be true, and therefore cannot warn the user, much less take evasive action, when confronted with counterfeit signals.
While the GPS P-code is encrypted and thus, is difficult to spoof, the civilian GPS signal, the C/A code (and other non-encrypted GNSS codes), are relatively easy to spoof because the signal structure, the spread spectrum codes, and modulation methods are open to the public. Insecure civil GPS technology has recently been utilized by critical systems, such as communications systems, banking and finance institutions, and the power grid. Consequently, these systems could be severely compromised when subjected to a spoofing attack resulting in positioning or timing anomalies that may further cause critical system degradation or disruption.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
Embodiments are described, by way of example only, with reference to the accompanying drawings. Further, the accompanying drawings, which are incorporated herein and form part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the disclosure and to enable a person skilled in the relevant art(s) to make and use embodiments thereof.